1. Field of the Invention
The present invention relates to an electrode, a lithium battery using the same, and a method of manufacturing the same. More particularly, the present invention relates to an electrode having improved thermal stability and cycle characteristics, a lithium battery using the same, and a method of manufacturing the same.
2. Description of the Related Art
With the development of portable electronic equipment in recent years, there has been an increasing demand for batteries to be used therein as a power source. In particular, a lithium secondary battery that is capable of charging and discharging has been the focus of intense investigation.
A lithium secondary battery is generally configured to include an anode, a cathode, and a separator is interposed therebetween so as to prevent a short-circuit therebetween. An electrolyte is further included so as to provide a pathway for lithium ions between the electrodes (i.e., the cathode and the anode). As such, the lithium secondary battery produces electric energy by oxidation and reduction reactions, which take place when the lithium ions undergo intercalation and deintercalation in the cathode and the anode.
A lithium metallic battery in which metallic lithium or an alloy thereof is used as the anode leads to the following problem. When a short-circuit occurs due to a formation of dendrite, the lithium metallic battery may explode. Thus, lithium metallic batteries are being replaced by lithium ion batteries using a carbon material as an anode active material.
In the lithium ion battery, while maintaining the original form of an electrode active material thereof, only the lithium ions migrate back and forth during charging and discharging. As such, an improved battery cycling and safety characteristics are achieved as compared with the lithium metallic battery. However, as the requirements for high-capacity batteries have increased, battery safety is an active research area. In this regard, there needs to be functional materials for achieving stable batteries having a large capacity. Accordingly, most battery manufacturers have continued to concentrate on developing safe batteries.
An electrode of a lithium secondary battery is configured such that active material layers containing an active material, a binder, and a conductive agent are laminated on a current collector. Conventionally, fluorinated polymers, such as polyvinylidene fluoride (PVDF), copolymers of vinylidene fluoride and hexafluoropropylene, mixtures of PVDF and styrene-butadiene rubber (SBR) and the like, are generally used as a binder. These binders have good properties including a high impregnating capability of an electrolytic solution and a large adhesive strength between active materials. However, when a lithium secondary battery fabricated using such a fluorinated polymer singly as a binder is overcharged, the thermal stability of the battery deteriorates severely. This is because the fluorinated polymer reacts with the carbon or the graphite used as the anode active material and a large amount of heat is generated. This reaction results in a dehydrofluorination to the fluorinated polymer binder, or further fire or explosion of the battery, so that the battery may not be used any more.
In order to enhance the thermal stability of the fluorinated polymer binder, heat resistant silica (SiO2) filler particles may be added to the PVDF binder so as to fabricate a heat resistant electrode. However, in the case where SiO2 filler particles are present in an anode plate, the SiO2 filler particles, which are highly reactive with lithium, react with the lithium to form an intermetallic compound Li4Si. The irreversibility of the intermetallic compound sharply reduces the charge/discharge capacities with the progress of repeated cycling, which becomes more obvious for large-capacity, lithium secondary batteries. Thus, it is quite difficult to fabricate an anode plate with improved thermal stability while avoiding degrading the cycle characteristics just by adding SiO2 filler particles to an active material layer.